1. Technical Field
The present invention relates to an imaging apparatus for a thermal analyzer which images a heated sample inside a thermal analyzer from an observation window provided in the thermal analyzer and relates to a thermal analyzer provided with the imaging apparatus.
2. Description of the Related Art
Conventionally, as a method of evaluating temperature characteristics of a sample, there is known a method of a so-called thermal analysis in which a sample is heated and physical changes of the sample accompanied by temperature changes are measured. Thermal analysis is, for example, defined in JIS K 0129:2005 “Thermal Analysis General Rule” in which all the methods related to measuring physical characteristics of a sample while the temperature of a measurement target (sample) is controlled by a program are considered as thermal analysis. As a method of thermal analysis which is generally used, there are five methods, such as (1) a differential thermal analysis (DTA) for detecting a temperature (differential temperature), (2) a differential scanning calorimetry (DSC) for detecting a differential heat flow, (3) thermogravimetry (TG) for detecting mass (weight changes), (4) a thermo-mechanical analysis (TMA) for detecting dynamic characteristics, and (5) a dynamic mechanical analysis (DMA).
In the meantime, there have been requests hoping to observe a sample during thermal analysis, and therefore, there has been proposed a thermal analyzer that is provided with an observation window. As a technology of imaging a heated sample inside the thermal analyzer through the observation window, a thermal analyzer in which a telescope is installed facing the observation window and an optical axis from the telescope is bent to 90 degrees so as to be connected to a CCD camera has developed (cf. JP-A-2-1024440). According to the configuration disclosed in JP-A-2-1024440, since the CCD camera is arranged at a position apart from the high-temperature observation window in a vertical direction, it is possible to prevent the CCD camera from being damaged due to heat.
However, according to the configuration disclosed in JP-A-2-1024440, when an optical system such as a telescope or a mirror is arranged between an observation window (a sample therein) which is an imaging subject, and a camera so as to prohibit heat of the observation window from being directly applied to a camera lens, a distance between the sample and the lens increases. Generally, a distance between a sample S and a lens L is regulated by a working distance (operation distance) WD, and the WD is determined based on a magnitude of a viewing field V, a focal distance F of the lens, and a CCD size (size of an image on the CDD) I (cf. FIG. 2, which shows a configuration related to the present invention). Therefore, in order to arrange the optical system between the observation window and the camera, and to ensure resolution of an observation image of the sample S in a state where the WD is increased, the viewing field V may need to be constant. In this case, the focal distance F increases and a depth of field becomes shallow. Thus, fineness of the observation image is degraded with respect to irregularities of the sample S. In addition, the increased WD causes a disadvantage in that the configuration of the optical system increases in size or becomes complicated.
Moreover, when a camera is arranged above the observation window, if a transparent material (for example, quartz glass, heat resistant glass, and sapphire glass) is arranged therebetween for heat shielding, the transparent material and a furnace tube which is formed with a transparent material in a similar manner create a multi-layer, thereby causing a problem of a blurred observation image.